1. Field of the Invention
The present invention relates to a ball screw, and more particularly to a circulating assembly for a ball screw that can be assembled easily and quickly.
2. Description of the Prior Art
Nowadays, ball screw is used more and more widely in modern industries. As a linear transmission means, the ball screw not only has high precision but also has the advantages of low frictional loss, high energy conversion ratio, low noise and high rigidity. Hence, it is self-evident that the ball screw is very important to various industrial mechanisms.
In order for the balls between the screw and the nut to circulate smoothly and for relieving the stress therebetween, the nut is usually provided at both ends thereof with two circulation cassettes for cooperating with the threads of the screw and the balls. And the circulation cassette is a key structure for enabling the balls circulation from the screw and the nut. Therefore, how to develop an improved and competitive circulation cassette is the common goal that the manufactures are striving for.
The conventional circulating assemblies are essentially classified into two categories: axial assembly (as shown in FIG. 1), and radial assembly (not shown). Please refer to the following detailed description:
Axial assembly:
FIG. 1 shows a ball screw of axial assembly type disclosed in U.S. Pat. No. 4,357,838, which comprises: a nut 10, a screw 11, a plurality of balls 12 and a circulating element 13. The circulating element 13 is installed into the end surface of the nut 10 for guiding the balls 12 into the circulation hole (not shown) of the nut 10. A very important portion of the circulating element 13 is called nail portion 14 that inserts into the threads of the nut 10 for guiding the balls 12 into the nut 10, and the helical grooves can be jointed smoothly by the integrally formed nail portion 14 of the circulating element 13.
The balls 12 are installed in the nut by the following steps:                1. installing the circulating element 13 into the nut 10 via the axial end surface thereof;        2. inserting a sleeve 15 into the nut 10, so as to enable the installation of the balls 12 later on;,        3. installing the balls 12 into the helical groove of the nut 10, at this moment, the balls 12 are confined in the helical groove by the sleeve 15 without falling off;        4. inserting a shoulder portion 111 of a screw 11 having an open helical groove through the sleeve 15, screwing the screw 11 into the nut 10, at this moment, both ends of the helical groove of the screw 11 must be open (the helical groove must extend to the shoulder portion 111), then the balls 12 can be installed successfully;        5. pulling out the sleeve 15, and the installation of the balls 12 is finished.        
The balls 12 installation method and the design of the screw 11 have the following disadvantages:
First, although this circulating element 13 has the advantages of smooth rolling path and high rotation speed, since the nail portion 14 is engaged in the helical groove 101 of the screw 11, any end of the helical groove 101 must be open so as to facilitate the installation of the nail portion 14 of the circulating element 13. In other words, the helical groove must extend to the shoulder portion of the screw 11, and the helical groove leaves a notch in the in the abutting surface of the shoulder portion 111, as a result, the integrality of the diameter of the abutting surface is damaged (the outer periphery of the abutting surface on the shoulder portion 111 is not round). When both ends of the screw 11 are mounted on bearing seats of a machine (not shown), and the motor of the machine starts to rotate the screw 11, the rotation inertia will effect an axial load on both ends of the screw 11. And due to the integrality of the diameter of the abutting surface is damaged, the axial load cannot be evenly distributed on the both ends of the screw 11. This will generate great pressure against the end surface (not shown) of the bearing seats, causing damage to the bearing seats, as a result of that, the screw 11 will be deformed during rotation, adversely affecting the circulation of the rolling elements, but will reduce the service life of the screw shaft. Therefore, it is uneconomical.
Second, the sleeve 15 should be inserted in the nut before installing the balls 12, and then should be taken out of the nut carefully by rotating the screw 11, therefore, the assembling process is complicated and time-consuming.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.